Background: There is concern about public understanding of overdiagnosis in breast cancer screening, and uncertainty about the likely impact on screening participation.
Methods: In a population-based survey of 2272 women, we assessed understanding of overdiagnosis and screening intentions before and after exposure to an explanation of overdiagnosis, and one of the three information formats providing an estimate of the rate of overdiagnosis based on the findings of the UK Independent Review.
Results: Subjective and objective comprehension of overdiagnosis was moderate across information formats (64% and 57%, respectively). Following overdiagnosis information, 7% of women showed a decrease in screening intention, with a stronger effect among women below screening age (<47 years), and receiving the estimate of the rate of overdiagnosis in a simple ratio format (one life saved to three overdiagnoses).
Conclusions: Brief written information on overdiagnosis was incompletely understood, but reduced breast screening intentions in a proportion of women, regardless of comprehension. Subjective comprehension was lower among women who had not yet reached screening age but the deterrent effect was higher.